Problems with encoding - Aspect Ratio

[chanpreet]

Hi There

i am a newbie to the encoding world but decided to venture into it. but i have a problem and was hoping someone here would be able to help me.

i have read the guides and am able to encode videos without any probems but one. i will explain it below

I use gordian know, and usually work from DVDs. Use Dvd decrypter, dvd2avi etc to produce a file.

Most of the dvds i have noticed are in 16:9 ratio (from what dvd2avi tells me)

so i select the same in the bitrate section along with it being NTSC/PAL. i the crop the video using autocrop and Smart pixel.

and then encode by setting the resolution etc.

The problem i have is though my aspect error <1% my aspect ratio ranges from 2.5-2.7. Whereas 16:9 should be around 1.7

so the problem is that my end videos are widscreen with thick blank bars on the top and botton with an aspect ratio of around 2.7

some of the divx movies that i have seen do not have this, and they have relatively small black bars on top and botton.

now i am not sure if this behaviour is normal when using 16:9 and cropping , but i wanted to get some information on this.

is there any settin that i have to change or is this behaviour normal.

thanks for your help, much appreciated.

[jggimi]

Hello, and welcome to the forum.

DVDs are in one of two Display Aspect Ratios (DARs), 4:3 or 16:9. However, films can be in any number of aspect ratios, such as Cinemascope (2.66:1, 2.55:1, 2.35:1) or Cinerama (3:1, 2.77:1, 2.59:1).

The DVD authors must add letterboxing or pillarboxing to the image in order to get it to either 4:3 or 16:9. The DVD video stream includes these black areas because there are only two DARs possible.

Widescreen films may have 4:3 DARs ... I have a collection shot in Todd-AO (2.22:1) that all have 4:3 DARs. This means they have a lot more letterboxing than if they had been properly authored with 16:9 DAR.

[chanpreet]

Thanks jggimi

The output i get in the end (a divx file) after encoding a dvd rip is expected to have thick black boxes if the original dvd is encoded with 16:9?

The problem i face is that my my dvd is in 16:9 format which equates to an aspect ratio of 1.77 : 1

My final divx file(after cropping) has an aspect ratio of around 2.5

the divx file plays alright, but has thick black bars on the top and bottom.

so i wanted to know if this is a normal behaviour

i will include osme screen shots to keep more clear.

cheers

[jggimi]

The video stream from the DVD will have some letterboxing or pillarboxing, unless the content is exactly 4:3 or 16:9. If you look at the preview window in Gordian Knot before cropping, you will see these black bars. They are part of the video on the DVD.

When you crop in GKnot, it will remove these black bars. Unlike the DVD, the .avi will not have any letterboxing in it. It will, however, be in square pixels, having been resized based upon the DVD's DAR.

Your final frame size after resizing should be somewhat close to the original aspect ratio of the film. It won't be exact, because of the modulo values used by Gknot for resizing (16 and 32 pixels).

Sometimes, the DVD packaging will have the film's aspect ratio printed on it. Or, you can look up the film's technical details (and DVD details) at the Internet Movie Database (www.imdb.com).

[manono]

Hi-

The problem i face is that my my dvd is in 16:9 format which equates to an aspect ratio of 1.77 : 1

Yeah, you're confusing the DAR (=Display Aspect Ratio, or how the DVD player resizes the movie) with the movie's Aspect Ratio. Evidently you have some 2.35:1 movies which are closer to 2.40:1 or 2.45:1, and after you crop and resize them to get low Aspect Error, they may become 2.50:1 (for example, 640x256). I don't know how you're cropping and resizing, but the Smart Crop All can do this. As long as you've filled in NTSC or PAL, and 4:3 or 16:9 from DVD2AVI, correctly, and have cropped and resized to achieve low Aspect Error, then you're OK. However, I think that, for example, 640x256 is also too narrow. There are a couple of ways around it. One is to make the W-Module Mod 16, and make it 656x272. That's about 2.41:1 and is pretty close to the AR of a lot of movies these days.

Here's another, and in some ways better, way. Use the Pixel Crop to crop away all the black. At that point it may have an Aspect Ratio of 2.42:1 or so, and an Aspect Error of 2% or so. Then start cropping from the left and right sides to achieve low Aspect Error. That will give you 640x272, or 2.35:1, if 640 is your chosen Horizontal Resolution.

There are some cases where the movie's AR is the same as the DAR of 16:9 or 1.77:1. And as jggimi said, they ordinarily will have no black bars at all. But they are rare. More common is 1.85:1. But the most common widescreen AR is the so-called 2.35:1 movie, which is often more narrow than that.